Energy couplers are known that couple energy to or from a transmission line to allow test equipment or other analysis equipment to monitor information being communicated over transmission lines, such as coaxial cables. In addition, energy couplers are used to inject energy onto transmission lines, if desired or "splits" signals. For example, with wireless communication systems, conventional energy couplers are often connected in-line with transmission lines that are embedded in coaxial cables to determine system performance and to split signals. If couplers have low coupling coefficients, high losses can result. In addition, certain applications, such as those involving delay lines, require proper impedance matching to avoid changes in delay times. Accordingly, energy couplers should provide the ability to facilitate relatively easy impedance matching. It is desirable to minimize power losses due to energy coupling and to provide an optimized power efficiency for couplers to avoid power losses.
One known type of energy coupler, sometimes referred to as a planar strip line coupler, uses a non-adjustable planar microstrip that is connected in series with a transmission line at a terminal connection of a transmission line such as a coaxial cable. A second wire is placed in close proximity to the planar microstrip on a printed circuit board and serves as a coupling line. These planar strip line couplers typically provide a fixed coupling coefficient with the coaxial transmission line, and are typically inserted in-line (in series) with the coaxial transmission line. Such planar strip line couplers provide fixed coupling coefficients and need to be inserted, re-moved at different points along a coaxial cable, and reinserted until a suitable coupling coefficient is reached.
Another known type of energy coupler include s a two-wire coaxial coupler which typically includes two wires in a twisted pair format that are placed in-line with the coaxial cable. This configuration also provides a fixed coupling coefficient and also has to be connected in series with the coaxial cable transmission line. Such two wire coaxial couplers may be physically cut in different length to provide a different fixed coupling coefficient. However, such length adjustment can become cumbersome.
In addition, other energy couplers are known that may provide a pin that may be manually adjusted so that its distance varies with respect to the coaxial transmission line to change the coupling coefficient. However, the pins can be difficult to manually adjust and may not provide a suitable range of differing coupling coefficients.
Accordingly, a need exists for an energy coupler that is relatively inexpensive and compact in size that provides an adjustable coupling coefficient.